The invention relates to machine tools in general, and more particularly to improvements in grinding and like machines which employ material removing wheels. Still more particularly, the invention relates to improvements in so-called wheelheads which can be used in universal or special grinding and like machines to treat workpieces by means of several material removing wheels.
It is often desirable and advantageous to treat each of a series of successive workpieces by two or more grinding wheels, for example, to carry out a preliminary grinding operation with a coarse-grained grinding wheel and to complete the grinding operation (i.e., to carry out the so-called finish grinding) with a fine-grained grinding wheel. In order to save time and to reduce the down times of the machine, it is desirable to complete a multi-stage grinding operation without detaching the workpiece from its support, e.g., without removing the workpiece from the space between the centers of a headstock and a tailstock. Heretofore known proposals to accomplish such objects include the utilization of wheelhead with a single spindle and with means for separably mounting on the spindle any one of a plurality of different grinding wheels so that a wheel for coarse grinding must be removed upon completion of a preliminary grinding operation in order to provide room for a different wheel which is designed for finish grinding. A drawback of this proposal is that the treatment of each and every workpiece (which must be subjected to a series of different treatments involving the use of different grinding wheels) necessitates at least two exchanges of grinding wheels with attendant long intervals of idleness of the machine. Furthermore, each exchange of grinding wheels invariably involves some radial deviation of the mounted grinding wheel (i.e., the freshly mounted grinding wheel runs out of true) so that, if a workpiece is to be ground with a high or reasonably high degree of precision, it is necessary to dress each and every freshly mounted grinding wheel before the freshly mounted grinding wheel comes in contact with a workpiece.
In accordance with another prior proposal, the wheelhead is provided with two spindles each of which can carry a single grinding wheel. The wheelhead can be indexed between two positions in one of which the wheel on one of the spindles is ready to remove material from a workpiece and in the other of which the wheel on the other spindle can be caused to contact a properly mounted workpiece. Such proposal is quite satisfactory except that the cost of a wheelhead with two spindles is quite high and the wheelhead with two spindles takes up a substantial amount of space.
In accordance with a further proposal, the grinding machine is equipped with two wheelheads each of which carries a single spindle for a single grinding wheel. This solution also exhibits the drawback that the two wheelheads occupy too much space and contribute significantly to the initial and maintenance cost of the machine.